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Ratproxy, released under an Apache 2.0 software license, looks for a variety of coding problems in Web applications, such as errors that could allow a cross-site scripting attack or cause caching problems.

"We decided to make this tool freely available as open source because we feel it will be a valuable contribution to the information security community, helping advance the community's understanding of security challenges associated with contemporary Web technologies," wrote Google security expert Michal Zalewski on a company security blog.

Ratproxy -- released as Version 1.51 beta -- is quicker and less intrusive than other scanners because it is passive and does not generate a high volume of attack-simulating traffic when running, Zalewski wrote. Active scanners can cause problems with application performance.

The tool sniffs content and can pick out snippets of JavaScript from style sheets. It also supports Secure Sockets Layer scanning, among other features.

Since it runs in a passive mode, Ratproxy highlights areas of concern that "are not necessarily indicative of actual security flaws," Zalewski wrote. "The information gathered during a testing session should be then interpreted by a security professional with a good understanding of the common problems and security models employed in Web applications."

Google has posted an overview of Ratproxy as well as a download link to the source code. Code licensed under the Apache 2.0 license may be incorporated in derivative works, including commercial ones, but the origin of the code must be acknowledged.

Weak Web application security continues to embarrass companies, potentially causing the loss of customer or financial data.

A 2006 survey by the Web Application Security Consortium found that 85.57% of 31,373 sites were vulnerable to cross-site scripting attacks, 26.38% were vulnerable to SQL injection, and 15.7% had other faults that could lead to data loss.

As a result, security vendors have moved to fill the need for better security tools, with large technology companies acquiring smaller, specialized companies in the field.

In June 2007, IBM bought Watchfire Corp., a company that focused on Web-application vulnerability scanning, data protection and compliance auditing. Two weeks later, Hewlett-Packard Co. said it would buy SPI Dynamics Inc., a rival of Watchfire whose software also looks for vulnerabilities in Web applications in addition to performing compliance audits.